During the processing of workpieces on a machine tool, for example during cutting of workpieces by means of a high-energy beam, it is typically necessary to know the material type (for example construction steel, stainless steels, nonferrous metal, etc.) as well as the surface condition (for example oxidation of the surface, roughness, coating of the surface for example with paint or film, etc.) of the workpiece, to suitably adapt processing parameters such as, for example, advance rate, laser power, gas type and gas pressure. The material type or the surface condition of a workpiece to be processed is typically indicated manually by an operator of the machine tool. If the operator indicates to the machine tool a material type or a surface condition that does not correspond to the actual material type to be processed or the surface condition of the workpiece to be processed, this typically leads to an inferior outcome of the processing operation.
German Patent Publication DE 10 2011 005 907 B3 has disclosed a method for determining the reflectivity of a surface, which is illuminated with incident illumination, images of the surface being recorded with different illumination times and determining the bright surface proportion in which a predetermined minimum brightness is achieved in each of the recorded images. From the bright surface proportion determined, as a function of the different exposure times, the variation of the bright surface proportion with the exposure time is determined, and the reflectivity of the surface is determined therefrom to identify and distinguish between highly reflective and matte surfaces.